Modeling applications may let users create system models in a free-form environment that does not restrict the user to creating models of a certain order (e.g., a first order system model or a first order system model with time delay). Free-form environments may instead let a user create system models of almost any order and/or type. At times, users may find these free-form models difficult to work with.
For example, users may find it difficult to design controllers for system models developed in the free-form environment. Controller design may be difficult because the user may have to specify the controller in terms of certain parameters that may be non-intuitive.
Assume that the user wishes to implement a proportional integral derivative (PID) controller for a system model developed in the free-form environment. The user may have desired characteristics in mind for the controller, such as a phase margin, or a closed-loop response speed. Conventional applications may require that the user relate these desired controller characteristics to particular values for P, I and D gains that are used to design the controller. Relating desired characteristics to values of P, I, and D may prove difficult for the user because the relation of gains for P, I and D to the desired characteristics (e.g., phase margin or closed-loop response speed) is complex, nonlinear, and non-intuitive to the average user of a free-form modeling application. These difficulties may cause the user to resort to trial-and-error guesswork for values of P, I and D in the hopes that he/she eventually designs a controller that achieves an acceptable, or desired, response for the feedback system (i.e., the combination of the controller and the system).
Difficulties faced by users of free-form modeling environments when designing controllers for free-form models may discourage users from making use of free-form environments for designing certain types of controllers, such as complex controllers.